Well, I will start with the fuel filter, then i will check the cat., then onto the O2 sensor. and thanks for the replies........

It could be a restriction in the exhaust such as the catylitic converter. Is the car going into overdrive? does it seem to run good or does it hesitate at all?

Hello, Yes it goes into overdrive, and there seems to be no hesitation, it runs good, just the mpg is really lousy. I will check a few things out this week, like i said earlier, and go from there...Thank-you all,,,,,,,,,,

Oh Fuel filter I knew I had something on my to-do list for it

Well, you're halfway to a good tune-up. You've done plugs, wires, and the air filter. Do check your front O2 sensor, as that'* the likely MPG eater. If problems persist, I'd also clean the MAF sensor, then maybe try a can of Seafoam.

Since you're doing a full tune-up, don't forget about the non-fuel economy-related items: replacing the fuel filter, inspecting/replacing the PCV valve, and changing any fluids that are due for it (coolant, oil/filter, tranny fluid/filter).

Hello again, i will have to check that O2 sensor, a few people have mentioned it. Did the coolant, also the oil changes, and going to do the tranny fluid change soon. I will have to look into the seafoam stuff, don't know much about it. Thanks again....

If your going to do the seafoam, do it before you change the O2 sensor.

Don't focus entirely on the engine, a bad converter can hurt mileage also, try checking the brakes for dragging and wheel alignment, also low tire tire pressures will affect mileage.
Might be worth checking for fuel leaks as well, a weeping fuel line might not be as obvious as you'd think.